All three cameras you mention are good. I think you have to consider your normal use as they are different cameras.

You can fit the SD850 and W90 in your pocket and always have it with you. I feel the camera you have with you is infinitely better than the greatest camera in the world sitting at home when a photo opportunity comes up.

I would prefer the SD850. Ithas a more useful zoom range, and that lens is excellent. But the Sony is cheaper and slimmer. The Sony takes proprietary memory and you get more for your money with SD. But you would still come out cheaper with the Sony.

The A720 is the more versatile camera. You have full manual controls to fall back on and the optical qualities of the A series have always been excellent for the price. The 6X zoom can be useful at times. You will have to wait for them to come in stock. If you pre-order you usually pay full price and they will come down quite a bit once several retailers have them in stock. I would probably opt for the A650 because I like the articulated LCD. I haven't done the math, but I would think the pixel density is about the same comparing a 12Mb 1/1.7 sensor to an 8Mp 1/2.5. 8Mp is fine for 11X 16, but 12Mp gives you more cropping versatility and maybe a tad better prints. You end up with 200 PPI with 8Mp and 250 from 12Mp uncropped. I find that 200 PPI is into the point of diminishing returns where it is very hard to see any improvement over that. And I can't see any at all under magnification over about 240. Optical viewfinders don't show the entire scene and I find I usually have to crop a little. 200 PPI is in the range where you will see quality differences in some photos if you decrease that.

Face recognition is one of the new hot toys. I don't like having a camera focus on anything but what is in the center target so I know where it is focused without having to consult the LCD. I would just turn it off.

You will like stabilization. You can handhold in much more limited light as long as you aren't dealing with subject motion. Most people coming from SLRs are disappointed with f2.8 to f5 digital cameras in limited light, and the stabilization helps buffer the transition.

It sounds like a good deal of your photos might fall into the landscape category and will be taken out of doors. You might want to consider something that has a wide angle capability. A Panasonic TZ-3 could provide that capability, but with the loss of an eye level optical viewfinder. The Canon SD 800IS also has a wide agle capability with a viewfinder.